Evidence in childhood helmet wearing

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Steady rider
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Re: Evidence in childhood helmet wearing

Post by Steady rider »

Complimentary evidence
Recent studies have also cast doubt on the reliability of published case control studies and meta-analyses regarding the effectiveness of bicycle helmets. Zeegers 2015 45 states that “Three cases could be found in the literature with sufficient data to assess both risk ratios and odds ratios: the Netherlands, Victoria (Australia) and Seattle (U.S.A). In all three cases, the problem of overestimation of the effectiveness of the helmet by using odds ratios did occur. The effect ranges from small (+ 8 %) to extremely large (> + 400 %). Contrary to the original claim of these studies, in two out of three cases the risk of getting a head injury proved not to be lower for helmeted cyclists. Moreover, in all three cases the risk of getting a non-head injury proved to be higher for cyclists with a helmet.”The Seattle study, Thompson et al 46 claimed, “The use of helmets can reduce the risk of head injury by 85%”. The 400% overestimation from the Seattle study shows the degree of error that can occur from using comparisons and odds ratio calculations.

(9) (PDF) Effects of bicycle helmet wearing on accident and injury rates. Available from: https://www.researchgate.net/publicatio ... jury_rates [accessed Apr 26 2021].
Zeekers reports a vary large overestimation for helmet effectiveness from the Seattle study. Could this apply to other studies from T&Rs work?
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pjclinch
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Re: Evidence in childhood helmet wearing

Post by pjclinch »

Steady rider wrote: 26 Apr 2021, 8:54am
Zeekers reports a vary large overestimation for helmet effectiveness from the Seattle study. Could this apply to other studies from T&Rs work?
I'm not going to pretend my stats are good enough to give a proper answer to that based on the paper, but what I would say is that if a case/control study on helmet efficacy hasn't gone to clear and great length to ensure that the case and control cohorts are as close to effectively interchangeable as makes no odds (as of course they would be in a blind/randomised drug trial) then there's a good chance it isn't worth much.

There have been attempts to do stuff like controlling through non-head injuries and that's a start, but I think there is still far too much variation in what constitutes "a cyclist" to be able to get good answers without more information about the rider and the context they ride in than if they had a helmet on and what were their injuries.

Case/control is only a benchmark if it's done properly. Self selecting cohorts are not "properly", self selecting cohorts with a tendency to rather different risk profiles (e.g., sportier riders are at more risk of crashing and also more likely to use helmets, or children of affluent families riding with adults in parks are at lower risk of nasty crashes and more likely to wear helmets than children of less affluent families riding with their peers on urban streets, and so on) are a very long way from "properly", and where the intervention is suspected to change the behaviour of at least some of the users, and the behaviour is itself a risk factor... Case/control simply isn't at all well suited to this job, at least with present methodologies.

Pete.
Often seen riding a bike around Dundee...
Steady rider
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Joined: 4 Jan 2009, 4:31pm

Re: Evidence in childhood helmet wearing

Post by Steady rider »

http://citeseerx.ist.psu.edu/viewdoc/do ... 1&type=pdf
Curnow in 2005 seems to have similar opinions.
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